Crust

1. Preheat oven to 350F/180C and grease a 9-inch springform pan then set aside. 
2. Ina. food processor pulse the Oreos until a fine crumb is formed or you can place them in a plastic bag and use a rolling pin to crush the Oreos. 
3. Once evenly combined add melted butter to crumbs. Mix until a wet sand texture is formed. Press into the bottom and slightly up the upsides of the prepared pan. Bake for 5-8 minutes to set the crust. Let cool on a wire rack and reduce oven temperature to 325F/ 163C.

Cheesecake

1. In the bowl of an electric mixer fitted with a paddle attachment or large bowl with a hand-held electric mixer beat the cream cheese for 3 minutes at low speed. It should be smooth with no lumps. Add the granulated sugar and beat for another 2 minutes at a low speed. Add the Baileys, sour cream, and vanilla extract- mixing until fully combined. Make sure to scrape the sides of the bowl to ensure everything is evenly combined.
2. Add in the eggs one at a time, mixing well after each addition. You should have a creamy batter with no lumps. Pour into the prepared pan. Place 9-inch springform pan in a 10-inch cake pan- place cake pan in roasting pan and fill roasting pan with hot water halfway up the sides of the cake pan. This prevents ANY water from getting in the cheesecake and you don't have to wrap everything with foil.
3. Bake for 1 hour and 10 minutes to 1 hour and 25 minutes, the middle 2 inches of the cheesecake should jiggle just a little bit. I like to use an instant-read thermometer to check the internal temperature is 140-145F.
4. Turn the oven off and open the door so it is cracked open, let the cheesecake cool in the oven for 45 minutes - 1 hour then take it out of the roasting pan and cool on a wire rack for another hour. Then wrap cheesecake with plastic wrap. Let chill in the fridge overnight or at least 6 hours.

Topping

1. In a medium saucepan over medium-low heat warm the heavy cream. In a bowl add the chocolate, after the cream is warmed pour on top of the chocolate. Let sit for 5 minutes then add butter. Whisk everything together until evenly combined and glossy whisk in Baileys until fully combined. 
2. Take the cheesecake out of the fridge and use an angled spatula to gently release the crust from the sides of the springform pan, then release the pan and use the spatula to gently release the crust from the bottom of the pan, if you wanted to serve it on a different plate. 
3. Pour chocolate ganache on top and pipe whipped cream around the edge, use a Microplane zester to grate chocolate on top of the whipped cream, if desired. Let chill for at least 30 minutes before serving. Use a hot clean knife to cut slices of cheesecake and clean the knife in between each slice. Store leftovers in the fridge for up to 5 days.